Intuitivet tests: Lay use of statistical information

Abstract

Normatively, a statistical pairwise comparison is a function of the mean, standard deviation (SD), and sample size of the data. In our experiment, 203 undergraduates compared product pairs and judged their confidence that one product was better than the other. We experimentally manipulated (within subjects) the average product ratings, the number of raters (sample size), and theSD of the ratings. Each factor had two levels selected, so that the same change in statistical power resulted from moving from the low to the high level. We also manipulated (between subjects) whether subjects were given only the product rating data as summarized in a statistical format or the summaries plus the raw ratings. Subjects gave the most weight to mean product ratings, less weight to sample size, and very little weight toSD. Providing subjects with raw data did not increase their use of sample size andSD, as predicted.

This project was supported by NSF Grant SES-03-25080 to the second author, NSF Grant REC-9720410 to the third author, and a Rutgers University excellence fellowship awarded to the first author